Developing novel strategies to increase the content of bioactive unsaturated fatty acids (FA) in ruminant-derived products requires a deeper understanding of rumen biohydrogenation and bacteria involved in this process. Although high-throughput pyrosequencing may allow for a great coverage of bacterial diversity, it has hardly been used to investigate the microbiology of ruminal FA metabolism. In this experiment, 454 pyrosequencing and a molecular fingerprinting technique (terminal restriction fragment length polymorphism; T-RFLP) were used concurrently to assess the effect of diet supplementation with marine algae (MA) on the rumen bacterial community of dairy sheep. Eleven lactating ewes were divided in 2 lots and offered a total mixed ration based on alfalfa hay and concentrate (40:60), supplemented with 0 (control) or 8 (MA) g of MA/kg of dry matter. After 54 d on treatments, animals were slaughtered and samples of rumen content and fluid were collected separately for microbial analysis. Pyrosequencing yielded a greater coverage of bacterial diversity than T-RFLP and allowed the identification of low abundant populations. Conversely, both molecular approaches pointed to similar conclusions and showed that relevant changes due to MA addition were observed within the major ruminal phyla, namely Bacteroidetes, Firmicutes, and Proteobacteria. Decreases in the abundance of unclassified Bacteroidales, Porphyromonadaceae, and Ruminococcaceae and increases in as-yet uncultured species of the family Succinivibrionaceae, might be related to a potential role of these groups in different pathways of rumen FA metabolism. Diet supplementation with MA, however, had no effect on the relative abundance of Butyrivibrio and Pseudobutyrivibrio genera. In addition, results from both 454 pyrosequencing and T-RFLP indicate that the effect of MA was rather consistent in rumen content or fluid samples, despite inherent differences between these fractions in their bacterial composition.

A number of studies in dairy cows have shown a relationship between milk fat depression (MFD) and alterations caused in lipogenic gene expression by dietary nutrients.However, information in small ruminants is not only scarce but also inconsistent. Therefore, this experiment was conducted in dairy ewes to study the effect of a diet known to induce MFD on milk fatty acid (FA) composition and mRNA abundance of key candidate genes involved in mammary lipogenesis. Twelve lactating Assaf ewes (63 days in milk; SD = 7.8) were randomly assigned to 2 treatments consisting of a total mixed ration based on alfalfa hay and concentrates (50:50), supplemented with 0 (control) or 17 g of fish oil/kg of diet DM (FO). Profiles of milk FA and mRNA abundance of candidate genes in biopsied mammary tissue were examined before starting the treatments and after 1 and 4.5 weeks on the diets. As expected, FO induced MFD and modified milk FA composition. Compared with the control, 3 reductions in milk fat concentration and yield were not detected on day 7, but reached up to 25 and 22%, respectively, on day 30. However, increases in confirmed or putative antilipogenic FA (trans-10 cis-12 and trans-9 cis-11 18:2, cis-9 16:1, cis-11 18:1 and oxo-FA) were already established on the early stage of the treatment and lasted until the end of the feeding period. These changes were accompanied by decreases in the mRNA abundance of genes encoding lipogenic enzymes. The coordinated nature of the downregulation, which tended to affect most studied metabolic pathways, including FA activation (ACSS2), de novo synthesis (ACACA and FASN), uptake and transport (LPL and FABP3), desaturation (SCD1) and esterification (AGAPT6), supports the involvement of a central regulator of milk fat synthesis. In this regard, without ruling out the potential contribution of PPARG, our results suggest that SREBF1 would have a relevant role in the MFD syndrome in sheep fed FO.Among the other studied transcription factors, the tendency to a downregulation of INSIG1 was associated with that of SREBF1, whereas no variation was detected for SCAP or THRSP.Fish oil had no significant effects on the transcript abundance of CD36, GPAM, DGAT1, LPIN1 and XDH. Overall, changes in potential antilipogenic FA and mRNA abundance of candidate lipogenic genes support a relationship between them and suggest that FO-induced MFD in dairy ewes would be mediated by transcriptional mechanisms.

There are very few studies in ruminants characterizing mammary and adipose tissue (AT) expression of genes and gene networks for diets causing variations in milk fatty acid (FA) composition without altering milk fat secretion, and even less complementing this information with data on tissue FA profiles. This work was conducted in sheep in order to investigate the response of the mammary gland and the subcutaneous and perirenal AT, in terms of FA profile and mRNA abundance of genes involved in lipid metabolism, to a diet known to modify milk FA composition. Ten lactating Assaf ewes were randomly assigned to two treatments consisting of a total mixed ration based on alfalfa hay and a concentrate (60 : 40) supplemented with 0 (control diet) or 25 (SO diet) g of sunflower oil/kg of diet dry matter for 7 weeks. Milk composition, including FA profile, was analysed after 48 days on treatments. On day 49, the animals were euthanized and tissue samples were collected to analyse FA and mRNA abundance of 16 candidate genes. Feeding SO did not affect animal performance but modified milk FA composition. Major changes included decreases in the concentration of FA derived from de novo synthesis (e.g. 12:0, 14:0 and 16:0) and increases in that of long-chain FA (e.g. 18:0, c9-18:1, trans-18:1 isomers and c9,t11-CLA); however, they were not accompanied by significant variations in the mRNA abundance of the studied lipogenic genes (i.e. ACACA, FASN, LPL, CD36, FABP3, SCD1 and SCD5) and transcription factors (SREBF1 and PPARG), or in the constituent FA of mammary tissue. Regarding the FA composition of AT, the little influence of SO did not appear to be linked to changes in gene mRNA abundance (decreases of GPAM and SREBF1 in both tissues, and of PPARG in the subcutaneous depot). Similarly, the great variation between AT (higher contents of saturated FA and trans-18:1 isomers in the perirenal, and of cis-18:1, c9,t11-CLA and n-3 PUFA in the subcutaneous AT) could not be related to differences in gene mRNA abundance due to tissue site (higher LPL and CD36, and lower SREBF1 in perirenal than in subcutaneous AT). Overall, these results suggest a marginal contribution of gene expression to the nutritional regulation of lipid metabolism in these tissues, at least with the examined diets and after 7 weeks on treatments. It cannot be ruled out, however, that the response to SO is mediated by other genes or post-transcriptional mechanisms.